High phosphorus levels and siltation continue to be the main concerns for the health of Highland’s Silver Lake, according to a recently released preliminary study of the lake’s water quality.
Peter Berrini, the author of the city-commissioned study, said some steps have already been taken to combat the problems, but there is more — likely expensive — work that needs to be done.
“Several things were done to stop erosion in the past,” said Berrini. “We installed 4,000 feet of bedrock to protect the shoreline.”
But more steps are needed to reduce phosphorus levels in the 550-acre lake, Berrini said.
“Total phosphorus concentration on average is over .23 (milligrams per liter),” Berrini said. “When phosphorus is over .2 on a consistent basis, that is very high. That means it’s readily available for algae to grow.”
Blue-green algae feeds off phosphorus, which enters the lake via erosion from the 30,688 acre-wide watershed, surrounding farmlands, and from the lake itself.
This type of algae is typically harmless, but can influence the taste of drinking water and cause a slight skin irritation if exposed to for too long. The algae reduces the visibility of the lake to less than a foot. This makes it nearly impossible for sunlight to penetrate the water, and underwater plants can’t grow easily. Without the plants, oxygen levels in the lake are reduced, which leads to a decrease in the fish population.
If phosphorus levels are reduced, the blue-green algae will start to die off.
In 2008, four solar-powered, aeration units were installed to mix and aerate the lower portion of Silver Lake, but only two of the four are currently operational. However, these devices only make it more difficult for algae to grow; they don’t reduce phosphorus levels.
Berrini said there is “no silver bullet” to reducing phosphorus levels in the lake, but instead recommends the City Council implement multiple options to accomplish this, including:
▪ Repair the two inoperable Solar Bees so that all four units can operate as originally designed.
“Two operating units out of four are not sufficient,” Berrini said in his report.
▪ Plan and implement the restoration of the eroded peninsula located north of I-70. Floating wetland islands can typically cost in excess of $35 per square foot. The most cost-effective scenario would likely include a select number of island pods connected by a combination of other materials.
▪ Dredge approximately 70,000 to 80,000 cubic yards of soft sediment from the upper end of the lake in order to minimize sediment and phosphorus re-suspension and subsequent transport to the lower portions of the lake.
“An in-lake option to reduce soft sediment re-mobilization and excessive phosphorus loading is selective dredging in the shallow upper end of the lake,” Berrini said. “That will trap and/or filter suspended sediment and phosphorus within the upper end of the lake.”
Berrini speculated dredging may cost up to $800,000.
▪ Complete a gully erosion survey using historical aerial imagery and a watershed windshield survey to identify the locations of reoccurring gully erosion. The cost of the proposed gully erosion survey is $5,000.
▪ Coordinate with the Madison County Soil and Water Conservation District (SWCD) to promote the use of cover crops and conservation tillage practices.
▪ Identify a minimum of five specific stream bank erosion sites to evaluate and prioritize for short-term planning and implementation efforts.
▪ Active participation in the Illinois EPA Volunteer Lake Monitoring Program (VLMP) was strongly recommended, with the intent of getting re-certified as a Tier 2 or Tier 3 monitoring participant to collect more intensive water quality data.
“(There’s) no question about (Silver Lake’s) economic importance. The lake is a great resource,” Berrini said. “Let’s protect it. There is value to this lake, and Highland is lucky to have it. It is a very, valuable local resource.”
After hearing the results, the City Council decided to discuss the options further and figure out which ones would be the most efficient and feasible for the city.
Other Council Action
Bid Awarded for Street & Alley building
The bid for the Street & Alley storage building was awarded to EAHC Structures in Effingham, in the amount of $89,970. EAHC Structures built the existing salt storage building in 2009. The proposed building is a larger version of the salt storage building.
Bids sought for Silver Lake boat ramp
The council approved seeking bids for a new boat ramp on the north end of Silver Lake.
The oil release of July 2015 showed the need for access onto Silver Lake north of Interstate 70.
Plains All American Pipeline, the company responsible for the oil spill last summer, has been working with the city to develop a new boat ramp, parking/staging area, and storage building for containment. The city hired Curry and Associates in May to prepare plans and specifications for public bidding.
Plains All-American Pipeline has agreed to fully fund the construction of the improvements.